The present invention is related to pager receivers, in general, and more particularly, to a pager receiver having a sequential lock-out circuit, an out-of-range circuit, and a common timer circuit for selectively generating the timing periods therefor.
For a paging system which has users spread over a very large geographical region, a radio frequency (RF) transmission system must be devised with a radiation pattern which blankets the entire region in order to reach each of the users. It is well recognized that the use of one large transmitter centrally located within the region would be at best considered cost prohibitive. Accordingly, paging systems have adopted the use of several smaller transmitters strategically located within the geographical region to offer individual radiation patterns which cover the region. Such a system is illustrated in the sketch of FIG. 1 wherein three transmission antennas designated as A1, A2, and A3 are disposed strategically to cover all of the pager users within a given area.
Normally, the different transmitters A1, A2, and A3, for example, transmit the same queue of pages sequentially over mutually exclusive periods of time. Because of the circular or omnidirectional radiation transmitting pattern of the antenna transmitters A1, A2, and A3 as shown by the boundary lines 11, 12, and 13, overlapping transmission areas of radiation are created. A pager receiver such as that shown by the "X" at P1 located in an overlapped area will receive a page transmission first from transmitter A1 and then the same page transmission from transmitter A2 sequentially thereafter. This duplication of page transmissions will cause the same alert annunciation to occur at different times in the pager P1.
In order to deal with this problem of unwanted duplicate alerts, some pagers have been designed with sequential lock-out circuits which inhibit the alert annunciation of repeat address function detects for a period of time that is commensurate with the maximum transmitted queue of a transmitter. A lock-out circuit may be included for each address function programmed into a pager such that each may be locked out independently of the other different address functions.
In addition, once the pager user moves to a location out of the composite radiation pattern, such as those locations shown at P2 and P3 in the illustration of FIG. 1, an out-of-range circuit disposed in the pager detects that it has not received a transmission over a predetermined period of time and, as a result, initiates an alert annunciation corresponding to an out-of-range situation. Of course, once the pager user moves to a location within a radiation pattern of one of the several antennas of the paging system, the out-of-range circuit is reset by the first received transmission and the annunciation corresponding thereto may be removed upon subsequent interrogation of the pager unit.
It is clear from the preceding description that, for each of the aforementioned circuits, some electronic timing mechanism is needed to establish the periods of time associated therewith. In most modern pager designs, timer circuits are usually comprised of a chain of digital divider networks which divide a reference oscillator frequency which may be on the order of 100 KHz or more down to periods of time associated with seconds and minutes. Moreover, circuit for establishing a time period is apparently needed for each address function detect which requires sequential lock-out and for the out-of-range detect circuit.
Not only does it become expensive in the number of circuit elements needed to implement the various individual timer circuits, but the duplication of timer circuits also requires a large area of real estate on an integrated circuit or on a printed circuit board, as the case may be. Power consumption is also a problem for energizing each of the individual timing generators with their long chains of flip-flop circuits, especially with regard to portable pagers that have an operational life which is heavily dependent on the power drain on the battery. To complicate matters further, custom decoding circuits are needed for each timer chain to identify the duration of the corresponding periods of time. Accordingly, because of the greater and greater emphasis on battery saving techniques and on designing pager electronics into a smaller profile, it is becoming of paramount importance to improve the aforementioned timer circuit designs of the pager and bring them in line with these power conservation and miniaturization trends. These objectives, as well as cost reduction, are the focus of the present invention which will be more fully understood from the following description of the preferred embodiment and drawings associated therewith.